The present invention relates to a method for manufacturing a bearing, and a bearing resulting therefrom, which is to be used under a high vacuum or under a high temperature such as in semiconductor manufacturing equipment.
Generally, bearings, when used under severe conditions such as vacuums, high temperatures and low temperatures, involve the use of solid lubricants. These solid lubricants are classified roughly into soft metal based ones, layered material based ones and high polymer based ones. Further, the soft metals are subdivided into gold, silver and lead, the layered materials are subdivided into MoS.sub.2 and graphite, and the high polymers are subdivided into PTFE (polytetrafluoroethylene), nylon, polyimide and the like. In particular, when the equipment employing the bearing is used under a high vacuum or high temperature, soft metal based solid lubricants are used, where silver is used for high temperatures by virtue of its superior durability and lead is used for ultra-low temperatures because it does not lose lubricity. Besides, with the use of a solid lubricant, too large a thickness of the solid lubricant would obstruct the rolling of the rolling element, while too thin a thickness would cause the lubricant to break. Accordingly, the thickness of the lubricant is adjusted to an appropriate one.
However, even with an appropriate thickness of the lubricant, if the adhesive strength of the lubricant to a surface to be lubricated is weak, the lubricant is more likely to break, resulting in a shortened service life of the bearing. On this account, in determining the bearing performance, adhesive strength of the coated lubricant onto the lubricated surface is a very important element for a decision as to the life of the bearing.
FIG. 2A is a partial sectional view of a ball 4 which is a conventional rolling element. For enhancement of the adhesive strength of a lubricant 12 to the ball 4, the ball 4 is cleaned with an organic solvent or the like so that contaminations such as fats and oils (not shown) are removed, and then the surface of the ball 4 is coated with the lubricant 12. Like this, the conventional bearing to be used under a high vacuum or high temperature has been manufactured through steps of cleaning the surface of the ball 4, the surface of a raceway (not shown), the surface of a cage (not shown) or the like with an organic solvent or the like, and thereafter coating the surface with a solid lubricant of silver, lead or the like, with the aim of increasing the adhesive strength of the lubricant 12 to the ball 4 or the raceway.
However, with the conventional bearing manufacturing method described above, although fats and oils or the like are relatively easily removed from the surfaces of the ball 4, the raceway and the like with an organic solvent, it is quite hard to remove oxide 11 from the surfaces. If the oxide 11 remains unremoved, there would occur a problem of deteriorated adhesion of the lubricant 12 due to the presence of the oxide 11. With deteriorated adhesion of the lubricant 12, a phenomenon would occur early that the coating of the lubricant 12 breaks during the rolling of the ball 4. Then, with the coating of the lubricant 12 broken, the ball 4 would make direct contact with the inner ring, the outer ring or the cage at the broken places, which would cause the rolling performance of the bearing to be considerably impaired. This would lead to a problem of shortened life of the bearing.